Archaea

Clusters of halobacterium strain NRC-1.NASA

Archaea:

Archaea are a group of microscopic organisms that were discovered in the early 1970s. Like bacteria, they are single-celled prokaryotes. Archaeans were originally thought to be bacteria until DNA analysis showed that they are different. In fact, they are so different that the discovery prompted scientists to come up with a new system for classifying life.

There is still much about archaeans that is not known. What we do know is that they can exist under some of the most extreme conditions, such as extremely hot, acidic, or alkaline environments.

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Three Domains:

Organisms are now classified into three Domains. The Domains are Eukaryota, Eubacteria, and Archaea.There are three main divisions of archaeans. These divisions are: Crenarchaeota, Euryarchaeota, and Korarchaeota.
Crenarchaeota:

Crenarchaeota consist mostly of hyperthermophiles and thermoacidophiles.Hyperthermophilic microorganisms live in extremely hot or cold environments.Thermoacidophiles are microscopic organisms that live in extremely hot and acidic environments. Their habitats have a pH between 5 and 1. You would find these organisms in hydrothermal vents and hot springs.

Crenarchaeota Species:

Examples of Crenarchaeotans include:

• Sulfolobus acidocaldarius - found near volcanic environments in hot, acidic springs containing sulfur.
• Pyrolobus fumarii - live in temperatures between 90 and 113 degrees Celsius.

Euryarchaeota:

Euryarchaeota organisms consist mostly of extreme halophiles and methanogens.Extreme halophilic organisms live in salty habitats. They need salty environments to survive. You would find these organisms in salt lakes or areas where sea water has evaporated.Methanogens require oxygen free (anaerobic) conditions in order to survive. They produce methane gas as a byproduct of metabolism. You would find these organisms in environments such as swamps, wetlands, the guts of animals (cow, deer, humans), and in sewage.

Euryarchaeota Species:

Examples of Euryarchaeotans include:

• Halobacterium - include several species of halophilic organisms that are found in salt lakes and high saline ocean environments.
• Methanococcus - Methanococcus jannaschii was the first genetically sequenced Archaean. This methanogen lives near hydrothermal vents.

Korarchaeota:

Korarchaeota organisms are thought to be very primitive life forms. Little is currently known about the major characteristics of these organisms. We do know that they are thermophilic and have been found in hot springs and obsidian pools.

Phylogeny:

Archaea are interesting organisms in that they have genes that are similar to both bacteria and eukaryotes. Phylogenetically speaking, archaea and bacteria are thought to have developed separately from a common ancestor.Eukaryotes are believed to have branched off from archaeans millions of years later. This suggests that archaeans are more closely related to eukayotes than bacteria.

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